Tracing troposphere-to-stratosphere transport above a mid-latitude deep convective system

[摘要] Within the project SPURT (trace gas measurements in the tropopauseregion) a variety of trace gases have been measured in situ in order to investigate the role of dynamical and chemical processesin the extra-tropical tropopause region. In this paper we report on a flight on 10 November 2001 leading from Hohn, Germany(52ºN) to Faro, Portugal (37ºN) through a strongly developed deep stratospheric intrusion. This streamer wasassociated with a large convective system over the western Mediterranean with potentially significanttroposphere-to-stratosphere transport. Along major parts of the flight we measured unexpectedly highNO_y mixing ratios. Also H₂O mixing ratios were significantly higher thanstratospheric background levels confirming the extraordinary chemical signature of the probed air masses in the interior of thestreamer. Backward trajectories encompassing the streamer enable to analyze the origin and physical characteristics of the airmasses and to trace troposphere-to-stratosphere transport. Near the western flank of the intrusion features caused by long rangetransport, such as tropospheric filaments characterized by sudden drops in theO₃ and NO_y mixing ratios and enhanced CO and H₂O can be reconstructed in great detailusing the reverse domain filling technique. These filaments indicate a high potential for subsequent mixing with thestratospheric air. At the south-western edge of the streamer a strong gradient in theNO_y and the O₃ mixing ratios coincides very well with a sharp gradient in potentialvorticity in the ECMWF fields. In contrast, in the interior of the streamer the observed highly elevatedNO_y and H₂O mixing ratios up to a potential temperature level of365 K and potential vorticity values of maximum 10 PVU cannot be explained in terms of resolved troposphere-to-stratospheretransport along the backward trajectories. Also mesoscale simulations with a High Resolution Model reveal no direct evidencefor convective H₂O injection up to this level. Elevated H₂O mixing ratios in the ECMWF and HRM model are seen onlyup to about tropopause height at 340 hPa and 270hPa, respectively, well below flight altitude of about200 hPa. However, forward tracing of the convective influence as identifiedby satellite brightness temperature measurements and counts of lightning strokes shows that during this part of the flight theaircraft was closely following the border of an air mass which was heavily impacted by convective activity over Spain and Algeria.This is evidence that deep convection at mid-latitudes may have a large impact on the tracer distribution of the lowermoststratosphere reaching well above the thunderstorms anvils as claimed by recent studies using cloud-resolving models.

[学科分类] 大气科学